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1. Total body water – Συνολική Ποσότητα Νερού (TBW) Body Composition (fat free mass and fat mass) can be calculated from body mass (weight) and TBW with an assumption that Fat-Free Mass (skeletal muscle) contains all the body water which comprises 730gr/Kg fat free mass Pros: This technique can be performed in any place Accuracy & repeatability are very high No side effects Cons: The cost and the technical difficulties associated with isotope analyses and The requirement for an isotope ratio mass spectrometer (φασματογράφο μάζας) and sample preparation systems often limit the use of this method 9

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Double Labeled Water 2H2O (Διπλά Συμασμένο Νερό) The procedure begins with a bolus administration of labeled water (diluted in 1-2 liters of tap water). Within two to three hours, the double water equilibrates with body water and provides a measure of the volume of the TBW pool. The labeled water is then excreted from the body through all routes of water loss. Samples from Blood, saliva or urine (24-hour urine collection) The amount of water NOT excreted is called Intracellular and the amount of water excreted is called extracellular 10 Protocol - Total body water (TBW)

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1.2 Extracellular water – Εξωκυτταρικό Νερό (ECW) with Sodium Bromide (NaBr) Extracellular water is physiologically important because it provides: 1.Environment for oxygen and nutrients transport 2.A route for clearance of cell metabolism Why is important to know the amount of ECW? 1.Calculate the “Intracellular water” (ICW) from Total Body Water 2.Assess the level of edema 11

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Extracellular water (ECW) with Sodium Bromide (NaBr) Why Bromide ? – Distributed in the extracellular space – Advantage of good absorption – Slow excretion – Low membrane penetration NaBr is distributed in the human body by intravenous injections Within two hours Bromide penetrates Red Blood Cells ECW can be calculated from the increase in Bromide concentration between baseline and post-dose blood samples. The amount of NaBr remains in the blood serum represents the ECW 12

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Total body potassium (TBK) BCM is considered the actively metabolizing portion of the body, which is known as MUSCLE Potassium is almost exclusively in intracellular space (95%) found chiefly in muscle (hence, essentially not found in fat, bone or extracellular water) Total body potassium (TBK) concentration is linearly correlated with the size of the BCM An accurate measure of BCM would prove extremely useful for establishing an individual’s state of health or disease over time, possibly assisting to the prevention of sarcopenia 14

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3. Body volume – Under Water Weighting – Υποβρύχια Ζύγιση (UWW) Used to be the “Gold Standard” for measuring body composition A technician submerges a person underwater The person exhales fully while underwater The technician measures the person’s weight under water 15

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Body volume – Under Water Weighting This equations assumes that Fat mass density is constant at different sites (0.007 g cm-3) which is correct Fat free mass is constant throughout the body (1.100 g cm-3) which is more problematic Bones always represents the 17% of the fat free mass Under the best circumstances, underwater weighting can estimate body fat within 2 –3% margin of error e.g. meaning that if your UWW test shows a 20% fat, this value could be no lower than 17% nor higher than 23% 17

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Body volume – Under Water Weighting Pros : Fairly accurate Inexpensive Cons : Time and labor intensive Often disliked by obese subjects Discomfort about being tested in the water tank Inability to perform maneuvers Required pool or water tank 18

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DEXA methodology The concept of DEXA is that: – Photon attenuation (εξασθένηση) in vivo is a function of tissue composition – The body is scanned with two different energies at the supine position, pixel by pixel – The ratio of the energy attenuation is calculated (R value) – DEXA systems assumes that the body consists of three components (fat, bone mineral, lean-soft tissue) that are distinguishable by X-ray attenuation 21

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5. Air Displacement Plethysmography (BOD POD) (πληθυσμογράφος αέρα) Plethysmography refers to the measurement of size, usually volume (όγκος) In air-displacement plethysmography, the volume of an object is measured indirectly by measuring the volume of air it displaces inside an enclosed chamber (plethysmograph). 23

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Air Displacement Plethysmography (BOD POD) Air-displacement Plethysmography offers several advantages over established reference methods, including a quick, comfortable, automated, noninvasive, and safe measurement process Accommodation of various subject types (eg, children, obese, elderly, and disabled persons) It is still expensive Accuracy is high only when it used multi dimensional measurements (more than one technique at the same time) 24

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Air Displacement Plethysmography (BOD POD) Human body volume is measured when a subject sits inside the chamber and displaces a volume of air equal to his or her body volume. Body volume is calculated indirectly by subtracting the volume of air remaining inside the chamber when the subject is inside, from the volume of air in the chamber when it is empty. The BOD-POD system includes the BOD POD plethysmograph, electronic weighing scale, calibration weights and cylinder, computer, and software. 25

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Body resistance – Bioelectrical Impedance Analysis (BIA) BIA measures the body impedance (αγωγιμότητα) using electrodes that are connected from one leg to the other leg or to the arm to form a circuit for the current to pass through BIA “predicts” total body water (TBW) and fat free mass (FFM) BIA estimations are based on the assumption that: The total body behaves as a cylindrical conductor with uniform cross-sectional area Human body has a homogenous composition with a specific resistance that is constant thought out the body 36

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Computer Tomography (CT) Very similar to what we can measure with MRI Different technology but similar results Different representation of the tissue (fat is dark, muscle is gray, bones are white) 45

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Summary The evaluation of body composition is a very important task and needs skilled personnel There are many ways for assessing body composition, however the selection of the appropriate approach is related to the studied population and the level of accuracy. 50

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